Among electric power adjustment systems that include a fuel cell, there is known an electric power adjustment system that is configured to supply an output power of the fuel cell to a load by supplying a fuel gas (such as hydrogen) and an oxidant gas (such as air) to the fuel cell in response to a request from the load that is connected to the fuel cell.
In the electric power adjustment system as described above, in order to control an operation state of the fuel cell, a wet/dry state (a wetness degree) of the fuel cell is estimated on the basis of an alternating-current component in an output current and an output voltage from the fuel cell that has a correlation relationship with the wet/dry state of the fuel cell, that is, an internal impedance of the fuel cell.
In the case where a ripple current included in the alternating-current component in the output current from the fuel cell is large when the wetness degree of a fuel cell stack is estimated on the basis of thus measured internal impedance, the wetness degree of the fuel cell cannot be accurately estimated, thereby causing difficulty in appropriately controlling the operation of the fuel cell.
Here, JP5143665B discloses an electric power adjustment system that includes a fuel cell and an electric storage device connected to a load in parallel, a first DC/DC converter disposed between the fuel cell and the load, and a second DC/DC converter disposed between the electric storage device and the load.
In this electric power adjustment system, according to a required electric power to the system, a transformation ratio of the first DC/DC converter is changed on the basis of a detection value of an output current from the electric storage device or a transformation ratio of the second DC/DC converter is changed on the basis of a detection value of an output current from the fuel cell. With this electric power adjustment system, controlling the transformation ratio of one of the two DC/DC converters ensures controlling a passing current of the other.